Filters with membranes of hollow fibers are employed for the most diverse purposes in the field of dialysis. For example, such filters are utilized for haemodialysis, in which blood is passed through the inside of hollow fibers constructed with semi-permeable walls and dialysis fluid is caused to flow past the outside of the hollow fibers. During this process, diverse convection and diffusion processes take place across the walls of the hollow fibers which result in cleansing of the blood and removal of superfluous fluid. Furthermore, the electrolyte concentration in the blood is conditioned and buffers such as bicarbonate or acetate, for example, are added to the blood.
Filters of this kind are also utilized for so-called haemofiltration, in which a substitution fluid is added to the blood. The blood is fed through the hollow fibers, but no dialysis fluid flows past the outer surface of the hollow fibers. In this case, superfluous fluid, in particular water, is removed from the blood solely with the aid of a pressure difference across the membrane, i.e. the semi-permeable wall of the hollow fibers. The substitution fluid can be added to the blood either before the filter or after the filter.
The above-mentioned filters can also be used for producing the substitution fluid itself; they are then called ultrafilters. In this case, water is fed through the hollow fibers and, by means of a pressure difference across the membrane or semi-permeable walls, filtered through the same; the water is filtered sterile by the removal of bacteria and endotoxins as well as other contamination products.
Further utilizations of the above-mentioned filters are, for example, hemodialiftration, a combination of hemodialysis and hemofiltratoin, and plasmapheresis, in which the aqueous blood plasma is filtered out of the blood and fed back into the blood after treatment. However such filters are also used for reverse osmosis.
Several processes are known for making filters with membranes. For example, a process is known from German Patent No. 28 24 898, in which several hollow fiber lengths are continuously combined to form a bundle. This bundle is then fed step-wise to a potting apparatus that pots a limited area of the fiber bundle with a potting compound so that a firm block is created that encloses the hollow fibers. In this way, by the step-wise advancing of the fiber bundle, firm areas or blocks are formed on the fiber length at predetermined distances. In the subsequent process, the fiber length is divided into individual bundles by severing each of the firm blocks through the middle. In this manner, individual bundles with firm end regions are created. These firm end regions are processed in a further step such that the fiber bundle enclosed in the firm region terminates with open ends. The thus formed fiber bundle is then put into a two-part housing. Subsequently, the two housing parts are brought together and firmly joined.
A disadvantage of this known process is the many process steps, which are expensive in terms of apparatus and cost. Furthermore, with this known process only bundles of one size for filters, or filter housings of one size, can be produced. To produce fiber bundles with different sizes for filters of different sizes the potting device must be replaced. This determines the size of the fiber bundle.
Furthermore, with this known process there is a high danger of contamination for the hollow fibers and the finished fiber bundle, as numerous processing steps are necessary and consequently much time passes before the hollow fibers or the fiber bundle is enclosed in the housing and sealed from the environment.
This is true for the filters manufactured with this process as well as for other filters, for which a fiber bundle is fabricated in several processing steps and subsequently combined with other parts to form a filter. Examples for such filters are disclosed in German Patent Nos. 28 44 941, 28 45 002 and 28 45 003. The filters disclosed therein are each composed of several frames holding fiber bundles. The individual frames with finished fiber bundles are set on top of one another and clamped together by means of clamps, which form the housing. By adding end portions that include connections for inlet and outlet, the filter is finally completed.
Another known process consists of the feeding of hollow fibers to a winding wheel and winding these in sleeve lower parts arranged on the outer circumference thereof by turning the wheel. As soon as the desired fiber bundle thickness or fiber bundle size has been reached, the winding wheel is stopped and the sleeve upper parts are placed on the sleeve lower parts and fixed there. Subsequently, the hollow fibers are cut between the sleeves, the sleeves are removed from the winding wheel and transferred to apparatus for taking the finished fiber bundles out of the sleeves and placing them into tubular filter casings.
This known process also has the disadvantage of numerous processing steps, so that in addition to the high constructional expense and the attendant cost there also exists a high danger of contamination of the finished fiber bundle, as has been described in detail above.
From U.S. Pat. No. 4,341,005, a process is known in which hollow fibers are fed to a winding wheel and are wound in first housing portions of a filter placed on the periphery of the winding wheel. If the first housing portions are full or slightly overfull, a second housing portion is placed over each fiber filled first housing portion. The two housing portions are secured together, and the hollow fibers between the housings are then cut. The housings are removed from the winding wheel, and the hollow fibers at the ends of the housings are thereafter potted by centrifugal castings, which also permits the potting compound to join with or to adhere to the housing walls as well as to the hollow fibers. Following this potting the ends of the hollow fibers are again cut in the area of the potting compound to re-expose the hollow cores and end caps are sealed onto the housings to complete the filter.
Even if with this known process the risk for contamination of the finished fiber bundle is reduced, this known process still has the disadvantage of numerous processing steps.
From U.S. Pat. No. 4,343,668, a more complex process is known, where a potting compound is applied at spaced intervalls on the hollow fibers during rotation of the winding wheel. This requires a complex device leading to high constructional expenses and attendant costs.
From U.S. Pat. No. 4,038,190, a process is known where hollow fibers are wound on a core, whereafter the core is placed in a housing.
This known process also has the disadvantage of numerous processing steps, so that in addition to the high constructional expenses and the attendant costs there is also a high risk for contamination of the finished fiber bundle as has been described in detail above.
In view of this background it is an object of the present invention to provide a method for producing filters with membranes of hollow fibers, for example for dialysis, whereby filters of any desired size can inexpensively and easily be reliably manufactured without excessive outlay, and with which the danger of contamination of the fiber bundle during fabrication of the filter is reduced.
A further object of the present invention is to provide a filter with membranes of hollow fibers, in which the hollow fibers are arranged essentially parallel to one another as a bundle in a tubular filter housing and that can be easily, inexpensively and reliably fabricated without excessive outlay.